The present invention relates to controlling reception of RF signals transmitted over a cable TV system and, more particularly, is directed to a remotely controlable system for mounting on the exterior of a subscriber dwelling or other structure to selectively permit or prevent reception of premium channels.
The cable television industry derives its income from the sale of subscription television programming transmitted via cable means from a location commonly termed a "headend." RF signals, normally received through a suitable antenna and down converter from one or more satellites in stationary orbit, are transmitted from the headend on a plurality of channels, some of which are designated as "basic" and others as "premium" channels. The cable means carrying the signals extends from the headend to the various subscriber locations for connection to television receivers adapted either by internal circuitry or by external converters to receive the channels carried on the cable. For an estblished, periodically payable fee, RF signals corresponding to the "basic" channels are received for broadcast on the subscriber's television set(s). Premium channels may also be received for viewing by the subscriber only if additional fees are paid to the cable transmitting service.
Since both basic and premium channels are carried by the same cable, means must be provided to permit reception and viewing of only those channels for which the required fee is paid. One such means for performing this function is through the use of devices known as traps. Conventional traps in current use fall generally into two categories, namely, negative traps which remove (or negate) a particular channel frequency which is not to be received, and positive traps which remove an interfering carrier which has been inserted at the headend from the spectrum of a particular channel. Thus, negative traps are included in the cable line between the headend and the subscriber's television set to prevent reception of one or more channels, while positive traps are connected in the line to permit reception of a particular channel without interference.
In any case, the control of reception of premium cable TV channels has required the physical installation and removal of traps at each subscriber location whenever reception of premium channels was initiated or terminated. Obviously, a considerable amount of inconvenience and cost is associated with sending a technician to a subscriber location to install or remove traps, which are often positioned at the top of a utility pole, each time premium channel service is changed. Therefore, although traps provide a very effective means of controlling channel access, and are relatively inexpensive and dependable devices, other means have been proposed in order to avoid the inconvenience and costs associated with their frequent installation and removal.
The most commonly used alternative to traps for providing channel security is electronic equipment which scrambles the RF signals carried by premium channels at the headend and descrambles at the subscriber location the signals on those channels for which the required fee has been paid. Descramblers are also generally divided into two general categories, i.e., programmable and addressable descramblers. Each scrambled channel has impressed upon it a unique electrical identification code, or program level. The programmable descrambler receives the scrambled signals and the accompanying identification code and, if it has been pre-set (programmed) to descramble signals at that program level, engages the restoration circuitry.
The addressable descrambler has a unique, coded address, usually built-in at the time of manufacture. A data stream including address and command codes is generated at the cable system headend and is received by the addressable descramblers at the subscriber locations. If the address code in the data stream matches the pre-set address of a particular descrambler, the premium channels indicated by the command code are descrambled. The appropriate codes are entered, in response to subscriber requests, into a computer terminal for transmission through appropriate interface devices to the addressable descramblers. Although the use of scramblers and descramblers has provided a convenient and cost-effective means of controlling access to premium channels, the advent of video recording systems (VCRs) has introduced a further difficulty. Since the descrambler is capable of processing only the particular channel to which the associated television receiver is tuned at a given time, if a scrambled channel is to be recorded, the descrambler must be in the circuit ahead of the VCR. If the subscriber wishes to view another, non-scrambled channel while the scrambled channel is being recorded, a device called a signal splitter must be installed in the line ahead of the descrambler to permit transmission of the non-scrambled channel directly to the receiver. The elements must be rewired to permit viewing a scrambled channel while recording a non-scrambled channel. In order to view and record two scrambled channel simultaneously, two descramblers are required with a signal splitter having outputs connected to each.
Rather than making the necessary wiring changes, most subscribers connect their descramblers and signal splitter in one of the aforementioned configurations and simply do not simultaneously view and record channels which that configuration is not equipped to handle. Instead, many subscribers terminate service on some or all of the premium channels and obtain the desired video recordings from tape rental outlets. This, of course, deprives the cable TV operators of a significant amount of revenue. Furthermore, the use of descramblers and converters may render many of the features of remotely-controlled, cable-ready television sets largely useless.
Thus, it is apparent that a need exists for a means to control access to premium channels which is not only cost-effective and dependable, but also does not deprive the subscriber of the benefits of conveniently viewing an recording all desired channels. The provision of such means is the principal object of the present invention.
A further object is to provide a cable TV channel security system using industry standard traps which do not require removal or installation in order to change the service provided to each subscriber.
Another object is to provide a system combining the advantages of transmitting signals over all channels of a cable TV network, including premium channels, "in-the-clear" (i.e., without scrambling and descrambling), and the capability of controlling access to premium channels from a remote location.
Still another object is to provide circuit means controlling access to cable-transmitted television signals on one or more predetermined channels wherein the circuit means are mounted in an enclosed housing on the exterior of a subscriber structure and are controlled to permit or prevent access to each of such channels from a remote location.
A still further object is to provide novel and improved means for packaging and interconnecting electrical circuit components selectively operable to permit or prevent reception of cable-transmitted, unscrambled RF signals on predetermined channels by a subscriber television receiver.
Another object is to provide novel circuit means for processing cable TV signals to control access by a subscriber television receiver of preselected channels.
Other objects will in part be obvious and will in part appear hereinafter.